add the ability to umount automounted devices from within the chroot

src/scripts/enter_chroot.sh

Index: src/scripts/enter_chroot.sh
diff --git a/src/scripts/enter_chroot.sh b/src/scripts/enter_chroot.sh
index 77b4722897b03262132f4132e14c53b74ced4bab..236aa02c090d1464355dc195f31c4669b99ac268 100755
--- a/src/scripts/enter_chroot.sh
+++ b/src/scripts/enter_chroot.sh
@@ -24,6 +24,8 @@ DEFINE_string build_number "" \
   "The build-bot build number (when called by buildbot only)." "b"
 DEFINE_string chrome_root "" \
   "The root of your chrome browser source. Should contain a 'src' subdir."
+DEFINE_string automount_dir "/media" \
+  "The directory in which your host OS creates mountpoints for external media."
 
 DEFINE_boolean official_build $FLAGS_FALSE \
   "Set CHROMEOS_OFFICIAL=1 for release builds."
@@ -100,6 +102,13 @@ function setup_env {
           die "Could not mount $MOUNTED_PATH"
     fi
 
+    MOUNTED_PATH="$(readlink -f "${FLAGS_chroot}${FLAGS_automount_dir}")"
+    if [ -z "$(mount | grep -F "on $MOUNTED_PATH ")" ]
+    then
+      sudo mount --bind "${FLAGS_automount_dir}" "$MOUNTED_PATH" || \
+          die "Could not mount $MOUNTED_PATH"
+    fi
+
     MOUNTED_PATH="$(readlink -f "${FLAGS_chroot}$CHROOT_TRUNK_DIR")"
     if [ -z "$(mount | grep -F "on $MOUNTED_PATH ")" ]
     then